Voltages and current transients are major causes of integrated circuit failure in electronic systems. Transients are generated from a variety of sources both internal and external to the system. For instance, common sources of transients include normal switching operations of power supplies, AC line fluctuations, lightning surges, and electrostatic discharge (ESD).
Transient voltage suppressors (TVS) are discrete devices commonly employed for protecting integrated circuits from damages due to the occurrences of transients or over-voltage conditions at the integrated circuit. Over-voltage protection are important for consumer devices or the Internet of Things devices as these electronic devices are exposed to frequent human handling and, as a result, may be susceptible to ESD or transient voltage events that may damage the devices.
In particular, the power supply pins and the data pins of the electronic devices both require protection from over-voltages conditions due to ESD events or switching and lightning transient events. Typically, the power supply pins needs high surge protection but can tolerate protection devices with higher capacitance. Meanwhile, the data pins, which may operate at high data speed, requires protection devices that provide surge protection with low capacitance as not to interfere with the data speed of the protected data pins.
Existing TVS protection circuits for high surge applications use vertical NPN or PNP bipolar transistor structures in open base configuration for bidirectional blocking. When a TVS is applied to protect the power line, it is important that the TVS has low leakage current. Leakage current through the TVS protection circuit may result in undesired power dissipation. Existing high surge TVS protection circuits decrease the leakage current by increasing the base doping level of the bipolar transistor. However, increased base doping decreases the gain of the bipolar transistor and compromises the clamping voltage due to lower bipolar injection efficiency.